1. Plant Disease
Diagnostic Clinic
C O R N E L L
UNIVERSITY
Basic
Plant Pathology
Karen L. Snover-Clift
Director, Plant Disease Diagnostic Clinic
Associate Director, NEPDN
Cornell University
Master Gardener Training
2. Plant Disease
Diagnostic Clinic
C O R N E L L
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Why is my plant sick?
• Evaluate each situation.
• Diagnose some diseases.
• Understand why certain disease management
situations are appropriate and others are not.
• Overall understanding of plant pathogens.
3. Plant Disease
Diagnostic Clinic
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Causal Agents of Disease.
Living vs. Non-living factors
•Fungi
•Bacteria
•Nematodes
•Viruses
•Phytoplamas
•Nutrient deficiencies
•Mineral toxicities
•Lack/excess of…
soil moisture & light
•Too low/high temperatures
•Air pollution
•Soil pH
4. Plant Disease
Diagnostic Clinic
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Definitions
PLANT DISEASE -- Any alteration in the
physiological processes of a plant, caused by living
organisms or nonliving agents, which negatively
affects the plant.
5. Plant Disease
Diagnostic Clinic
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PATHOGEN -- a pathogen is an organism that
is capable of changing the physiological
processes of a plant, thus causing disease.
PATHOGENIC means "disease causing"
6. Plant Disease
Diagnostic Clinic
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History of Plant Pathology
• 700 B.C.- The Romans sacrificed red dogs
and cattle to the Gods to rid their crops of rust.
• 470B.C.-Pliny reported that crushed olives
sprinkled on plants prevented blight.
• 1844-1845-The Irish Potato Famine prompts
the birth of modern plant pathology.
24. Plant Disease
Diagnostic Clinic
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History of Plant Pathology II
• 1885-Bordeaux Mixture
– Copper Sulphate/Lime and Downy Mildew.
25. Plant Disease
Diagnostic Clinic
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History of Plant Pathology III
• 1900- White Pine Blister Rust (WPBR), caused by
Cronartium ribicola, was introduced on seedlings
from European nurseries.
• White pines, especially young trees, and plants
belonging to the genus Ribes (currants and
gooseberries) are susceptible to the disease.
• Although WPBR is occasionally a severe foliar
disease on Ribes plants, on white pines it is
LETHAL if allowed to spread from an infected
branch into the trunk.
27. Plant Disease
Diagnostic Clinic
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White Pine Blister Rust
This disease caused the first US
quarantine in 1912. The following
wording was part of an update to the
act (Act 313 of 1929), “The cultivated
black currant is hereby declared a
public nuisance. Planting, possessing,
growing, propagating, selling or
offering for sale plants, roots, or
cuttings of cultivated black currants
within the state is hereby prohibited.
Such roots, cuttings or plants now
planted or growing may be destroyed
by the commissioner or his agents”.
28. Plant Disease
Diagnostic Clinic
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White Pine Blister Rust
“Current” information: Within
the blister rust hazard areas, all
susceptible Ribes should be
removed from the vicinity of
valuable white pines. Ribes are
not allowed to be planted in nine
northern counties of New York
and parts of 6 others (see
http://www.dec.state.ny.gov/regs/4079.html for more information). If
you wish to plant Ribes in New York State, contact the NYS Dept of
Agriculture & Markets Phone at 518-457-2087 before purchasing or
planting to determine if you can plant in your area.
29. Plant Disease
Diagnostic Clinic
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History of Plant Pathology III
• 1904-1940- Chestnut Blight- The disease wiped out
all the mature American Chestnuts in the eastern
North American states.
• The pathogen, Cryphonectria parasitica, was
brought in from the Orient on infected trees and was
first discovered at a zoo in NYC.
33. Plant Disease
Diagnostic Clinic
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History of Plant Pathology IV
• 1930-present-Dutch Elm Disease. This
disease devastated the street tree plantings
across the country.
• The disease was named Dutch Elm Disease
because it was first described in Holland in
1921.
• The pathogen, Ophiostoma novo-ulmi, was
first discovered in the US in Ohio.
39. Plant Disease
Diagnostic Clinic
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History of Plant Pathology V
• Golden Nematode, Globodera rostochiensis,
was discovered in 1941. It entered the country
on the tracks of WWI equipment returning
from Europe.
• It caused a slow decline in potato plants that
eventually lead to death.
• As of 1955, the distribution was believed to be
located only in Nassau and Suffolk counties in
NYS.
42. Plant Disease
Diagnostic Clinic
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Golden Nematode
After decades of building their population levels, the GN was
capable of reducing the potato yield up to 70%.
43. Plant Disease
Diagnostic Clinic
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Golden Nematode
For over 60 years, an effective Federal and State quarantine program
has confined the pest to nine counties in New York.
44. Plant Disease
Diagnostic Clinic
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History of Plant Pathology VI
• 1970-Southern Corn Leaf Blight, caused by Helminthosporium
maydis. Originally considered a minor disease, a change in the
genetics of seed corn caused an epidemic.
• In 1970, the disease was reported in every state east of the
Mississippi River, also in several states west of the Mississippi
River.
• The epidemic received enormous press coverage with over 37
articles printed in the Chicago Tribune alone.
• Losses due to the epidemic were officially estimated at nearly $1
billion nationally. Reduction in yield was greater in the South
versus the min-west corn belt states. In some areas damage caused
losses of 50-100%. Nationally losses averaged 20-30%.
47. Plant Disease
Diagnostic Clinic
Southern Corn Leaf Blight
C O R N E L L
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In an effort to reduce labor costs
associated with detasseling to
control pollination, breeders
incorporated cytoplasmic male
sterility, known as “Texas Male
Sterile Cytoplasm”, in the seed
corn. This inadvertently
included a high susceptibility to
the T race of the pathogen. This
seed was widely planted in
1970, resulting in devastating
outbreaks.
48. Plant Disease
Diagnostic Clinic
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History of Plant Pathology VII
• Sudden Oak Death, caused by Phytophthora ramorum,
was discovered in California.
• A large number of tanoaks were found to be declining
with no known cause. It took 5 years to identify the
pathogen that was causing the devastating damage.
• Also called ramorum blight and ramorum dieback.
• Although the disease was first observed in the United
States in tanoaks, it is also found to infect many,
many other plant species.
49. Plant Disease
Diagnostic Clinic
Sudden Oak Death
(Govt of British Columbia, Ministry of Ag, Food, & Fisheries)
• P. ramorum identified in
Germany and the Netherlands in
1993
•Sudden Oak Death named an a
disease in the US in 1995, the
pathogen identified as P. ramorum
5 years later by a UC Berkeley
researcher.
•In 2002, the isolates from the US
and UK are determined to be
different.
•P. ramorum found in HUGE
nursery in Los Angeles Co, CA.
50. Plant Disease
Diagnostic Clinic
Sudden Oak Death
• Nursery find sparked large
national survey, P.ramorum found
all over the country but only in
containerized plants.
•We learned that the understory
plants were the source of the
inoculum for infection
•Federal Order in place so that any
nurseries from CA, OR, and WA
wishing to ship outside of their
states must be inspected annually.
51. Plant Disease
Diagnostic Clinic
Common Regulated Hosts
Common Name Scientific Name
Japanese camellia Camellia japonica
Sasanqua camellia Camellia sasanqua
Witch Hazel Hamamelis virginiana
Himalaya pieris Pieris formosa
Pieris ‘Forest Flame’ Pieris formosa x japonica
Pieris ‘Brouwer’s Beauty’ Pieris floribunda x japonica
Japanese pieris Pieris japonica
Douglas-fir Pseudotsuga menziesii var. menziesii
Coast Live Oak Quercus agrifolia
Rhododendron (including azalea) Rhododendron spp
Bodnant Viburnum Viburnum x bodnantense
Doublefile Viburnum Viburnum plicatum var. tomentosum
52. Plant Disease
Diagnostic Clinic
Common Plants associated with P. ramorum
Common Name Scientific Name
Grand fir Abies grandis
Horse-chestnut Aesculus hippocastanum
Camellia Camellia reticulata
Camellia Camellia x williamsii
European beech Fagus sylvatica
Mountain laurel Kalmia latifolia
Drooping leucothoe Leucothoe fontanesiana
Chinese pieris Pieris formosa var. forrestii
Pieris Pieris formosa var. forrestii x Pieris japonica
Formosa firethorn Pyracantha koidzumii
Southern red oak Quercus falcata
Northern red oak Quercus rubra
Salmonberry Rubus spectabilis
Lilac Syringa vulgaris
David Viburnum Viburnum davidii
Fragrant Viburnum Viburnum farreri
Wayfaringtree Viburnum Viburnum lantana
Burkwood Viburnum Viburnum x burkwoodii
Prague Viburnum Viburnum x pragense
54. Plant Disease
Diagnostic Clinic
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History of Plant Pathology VIII
• 1999- Southern Wilt/Brown Rot, caused by Ralstonia
solancearum R3 B2
• Southern Wilt is a disease of Geranium and Brown Rot is
a disease of Potato
• Ralstonia solanacearum Race 3 Biovar 2 has appeared on
Geranium a few times in recent years but it appears to be
confined to greenhouse crops and there is no evidence of
spread to potato, tomato, or eggplant
55. Plant Disease
Diagnostic Clinic
Southern Wilt / Brown Rot
Photo Scott Bauer, USDA-ARS
• There are a number of races and
biotypes of this pathogen that
affect different plants.
•We are concerned with Race 3
Biovar 2 because it infects
solanaceous plants.
•It is also able to survive in
temperate climates and may be
able to overwinter in cull piles and
in plant debris or tubers left in
fields.
56. Plant Disease
Diagnostic Clinic
Southern Wilt / Brown Rot
Photo Peggy Greb, USDA-ARS
• The pathogen may be introduced
on infected geranium cuttings.
•Cuttings are produced overseas and
shipped here.
•They may be asymptomatic until
placed in warmer greenhouses for
rooting and then symptoms will
become present.
•In 2003, 127 greenhouse in 27
states received infected cutting from
a producer in Kenya.
•In 2004 , another introduction
occurred from a producer in
Guatamala.
(Wisconsin Department of Agriculture)
58. Plant Disease
Diagnostic Clinic
Foliar Wilting Bacterial Ooze
(Photos Central Science Laboratory, Crown Copyright)
Soil Adhesion
Symptoms
(Photo: Caitlin Allen, University of Wisconsin)
(Photos Central Science Laboratory, Crown Copyright)
59. Plant Disease
Diagnostic Clinic
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History of Plant Pathology X
• 1999- Plum Pox, caused by Plum Pox Virus, is a disease
of stone fruits caused by a viral pathogen called the Plum
Pox Virus
• Also known as “Sharka”
• First discovered in an Adams County, Pennsylvania
Orchard in 1999
• A member of the Agricultural Bioterrorism Select Agent
Listing of 2002. It was removed from the listing in April
2005 due to its limited ability to spread easily.
60. Plant Disease
Diagnostic Clinic
Plum Pox
(www.maf.govt.nz/.../ plants/plum-pox/)
• Plum Pox has been in Europe since
the early part of the century.
•First found in the US in Adams Co,
Pennsylvania in 1999 and in two
locations in Canada, Ontario and
Nova Scotia, in 2000.
•Surveys have been conducted in
NYS since 1999.
•Found in New York in 2006 and in
Michigan in 2006.
•Pennsylvania declared free of Plum
Pox in 2009.
61. Plant Disease
Diagnostic Clinic
Foliar Mottling
Fruit Spotting
Pit
Symptoms
Symptoms
John Hammond,
U.S. Department of Agriculture, Agricultural Research Service
62. Plant Disease
Diagnostic Clinic
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History of Plant Pathology XI
• 2004-Soybean Rust, is caused by two fungi named
Phakopsora pachyrhizi and Phakopsora meibomiae
• A member of the Agricultural Bioterrorism Select
Agent Listing of 2002. It was removed from the listing
in April 2005 due to its established presence in the US.
• P. pachyrhizi appeared in the US in November 2004,
apparently entering on winds of Hurricane Ivan. It was
found in 9 States shortly thereafter. Detected by a
NPDN exercise participant.
• It was found in Florida early in 2005 on Kudzu and
volunteer Soybean and new detections for this season
remained in the South.
63. Plant Disease
Diagnostic Clinic
Soybean Rust
• The pathogens that cause Soybean
Rust were originally found only in
tropical and sub-tropical areas of
Asia and Australia.
•In the 70’s and 80’s the pathogen
was found in Africa and South
America.
•Concern began when the pathogen
was discovered 5 degrees north of
the equator in Cali, Colombia in
August of 2004.
•Discovered in Louisiana by an
NPDN first detector in November
2004.
66. Plant Disease
Diagnostic Clinic
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Symptoms and their Causal Agents
Bacteria Fungi Viruses Nematodes Phytoplasmas
Wilts
Leaf Spots
& Blights
Fruit Rots
Root Rots
Damping Off
Distorted
Growth
68. Plant Disease
Diagnostic Clinic
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Parasites vs. Saprophyte
• Parasite- an organism that derives
nourishment from another living organism.
• Saprophyte- an organism that derives
nourishment from dead organic matter.
72. Plant Disease
Diagnostic Clinic
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Generalized Pathogen Lifecycle
Arrival on host
Germination
Penetration
Infection
Invasion
Reproduction
Overseasoning
Dissemination
2ºCycle
80. Plant Disease
Diagnostic Clinic
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Fungi
A fungus is a non-photosynthesizing eukaryote
that produces enzymes and absorbs its food;
usually producing and living inside a network of
apically extending, branching tubes called
hyphae. It produces reproductive structures
called spores.
95. Plant Disease
Diagnostic Clinic
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Fungi Spread
• Environmental Conditions
– Slight Air Movement to Wind, Splashing Rain
• Vectors
– People, Animals, Insects
• Planting Material
– Vegetative parts
• Mechanical Means
– Tools, Equipment, Plant Contact
96. Plant Disease
Diagnostic Clinic
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Fungi Management Techniques
• Fungicides
• Exclusion
• Eradication
• Resistant Varieties
• Clean Tools and Materials
• Avoid Wounds, Stress
98. Plant Disease
Diagnostic Clinic
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Bacteria
A bacterium (bacteria=plural) is a prokaryotic
single celled microscopic organism that
multiples by division.
103. Plant Disease
Diagnostic Clinic
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Bacterial Infection Routes
•Bacteria can infect plants through natural
openings and wounds.
112. Plant Disease
Diagnostic Clinic
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Bacteria Spread
• Environmental Conditions
– Splashing Rain
• Vectors
– People, Animals, Insects
• Mechanical Means
– Wounds by Tools and Equipment, Wounds by
Insect feeding
113. Plant Disease
Diagnostic Clinic
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Bacteria Management Techniques
• Bactericides used for protection
• Antibiotics
• Exclusion
• Eradication
• Resistant Varieties
• Clean Tools and Materials
• Avoid Wounds, Stress
114. Plant Disease
Diagnostic Clinic
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Viruses
A virus (viruses=plural) is made up of small
particles of genetic material encased in a
protein coat. They can only reproduce in a
living cell.
129. Plant Disease
Diagnostic Clinic
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Virus Spread
• Insects
– Aphids
– Leafhoppers
• Planting Material
– Vegetative parts
• Mechanical Means
– Tools
– Plant Contact
130. Plant Disease
Diagnostic Clinic
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Virus Management Techniques
• Insecticides
• Border Plantings/Removal of Weeds
• Rogueing Infected Plants
• Resistant Varieties
• Clean Tools and Materials
• Avoid Wounds.
131. Plant Disease
Diagnostic Clinic
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Nematodes
A nematode (nematodes=plural) is a
microscopic, worm-like animal that lives
saprophytically in water and soil or as
parasites of plants and animals
148. Plant Disease
Diagnostic Clinic
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Nematode Spread
• Environmental Conditions
– Splashing Rain, can swim short distances
• Vectors
– People and Animals moving soil and plant
parts, Insects within their bodies
• Planting Material
– Vegetative parts
149. Plant Disease
Diagnostic Clinic
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Nematode Management Techniques
• Nematicides
• Exclusion
• Eradication
• Resistant Varieties
• Clean Tools and Materials
• Avoid Wounds, Stress
151. Plant Disease
Diagnostic Clinic
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Phytoplasmas
• Phytoplasmas are organisms that infect
plants and cannot be grown in culture.
Phytoplasmas cause the “yellows” diseases.
153. Plant Disease
Diagnostic Clinic
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History of Phytoplasmas
• 1967-Japanese researchers associated
MLOs with “yellows” diseases.
• MLOs occupy sieve tubes.
• Graft and insect transmittable.
• Tetracycline causes remission and
temporary disappearance of MLOs.
154. Plant Disease
Diagnostic Clinic
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UNIVERSITY
Major Phytoplasmal diseases in North America.
• X disease of peaches and cherries.
• Lethal yellows of palm.
• Pear decline.
• Elm Yellows.
• Ash Yellows.
• Lilac witches broom.
• Aster Yellows.
• Blueberry witches broom.
• Bunch disease of pecan and walnut.
• Grapevine yellows.
155. Plant Disease
Diagnostic Clinic
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Phytoplasma-induced symptoms
• Slow to feeble growth
• Loss of apical
dominance
• Witches broomes
• Dwarfing
• Sterility
• Yellowing
•Rootlet Necrosis
•Phloem Necrosis
•Phloem hyperplasia
•Leaf malformation
•Impaired gas exchange
Diagnostic symptoms can be absent!!
165. Plant Disease
Diagnostic Clinic
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Phytoplasma Vectors
• Primarily Leafhoppers.
• Other known vectors include planthoppers,
psylids, a froghopper, and stinkbugs.
• Phytoplasmas circulate and multiply within
their vectors.
166. Plant Disease
Diagnostic Clinic
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Phytoplasma Management
Techniques
• Chemotherapy.
• Heat Treatments.
• Insecticides.
• Weed Control.
• Resistant Varieties.
167. Plant Disease
Diagnostic Clinic
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Abiotic Damage
• Herbicide Injury.
• Chemical Spills.
• Soil Compaction.
• Freeze Injury.
• Nutrient Deficiency.
• Air Pollution.
• Snow Damage.
